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My house has a circuit intended for outdoor lighting. There's a box in the joist of my basement labeled "post" and a switch by the front entrance that is connected to the box. The post was never installed so there's no wire to the outside from this box.
We'd like to put several light posts down along our driveway (550'). I am typing this without knowledge of the existing 'post' circuit's capacity but I think the electrician had not intended for this circuit to a) power more than one light post and b) run such a distance. Or maybe he did. What's required (wire gauge, circuit amp) for a run like this with, say, 5 outdoor lamp posts (with one bulb each)?
The switch and circuit left by the electrician is either 15 or 20 amp circuit. Find the breaker for this and check the handle, here you will see either 15 or 20 stamped on the handle.
The circuit size is fine for the post lights.
Your right to ask about the size wire needed for such a long distance. The wire size will need to be large enough to overcome the ressitance of wire to be able to deliver the proper amount of voltage to the end of the circuit.
To do actual voltage drop calcs, I would need to know the size lamp in each fixture, and the distance from home to the first postlight, and between each remaining post light.
My guess will be that #8 copper will be sufficient, #6 copper would be better, esp if there will be general purpose receptalces for portable tools or xmas lights.
If you find that copper wire costs is outrageous, then #4 aluminum will be fine. In any cae be sure the wire used has an insulation rated for wet locations, such THHN/THWN or XHHW. These are only for conduit.
If you don't use conduit, and want to direct bury cable, then use UF cable, or any wire that has USE insulation.
The switch and circuit left by the electrician is either 15 or 20 amp circuit. Find the breaker for this and check the handle, here you will see either 15 or 20 stamped on the handle.
The circuit size is fine for the post lights..
When you say the circuit size is fine you mean it's fine whether it's 15 or 20 amp?
Yes, that is exactly what I mean. Most likely the circuit is 15 amp, possible it is 20, and either is fine.
Now if you plan to add more load that the five post lights, plus whatever else is on the circuit, such as Xmas lights, then i suspect the circuit will be max'ed out quickly.
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